486,664 research outputs found
The Halo Density Profiles with Non-Standard N-body Simulations
We propose a new numerical procedure to simulate a single dark halo of any
size and mass in a hierarchical framework coupling the extended Press-Schechter
formalism (EPSF) to N-body simulations. The procedure consists of assigning
cosmological initial conditions to the particles of a single halo with a EPSF
technique and following only the dynamical evolution using a serial N-body
code. The computational box is fixed with a side of Mpc. This
allows to simulate galaxy cluster halos using appropriate scaling relations, to
ensure savings in computing time and code speed. The code can describe the
properties of halos composed of collisionless or collisional dark matter. For
collisionless Cold Dark Matter (CDM) particles the NFW profile is reproduced
for galactic halos as well as galaxy cluster halos. Using this numerical
technique we study some characteristics of halos assumed to be isolated or
placed in a cosmological context in presence of weak self-interacting dark
matter: the soft core formation and the core collapse. The self-interacting
dark matter cross section per unit mass is assumed to be inversely proportional
to the particle collision velocity: .Comment: Accepted for publication in MNRAS (2 figures added
The distribution of dark matter, galaxies, and the intergalactic medium in a cold dark matter dominated universe
The evolution and distribution of galaxies and the intergalactic medium (IGM) have been studied, along with collisionless dark matter in a Universe dominated by cold dark matter. The Einstein-deSitter universe with omega sub 0 = 1 and h = 0.5 was considered (here h = H sub 0 bar 100/kms/Mpc and H sub 0 is the present value of the Hubble constant). It is assumed that initially dark matter composes 90 pct and baryonic matter composes 10 pct of total mass, and that the primordial baryonic matter is comprised of H and He, with the abundance of He equal to 10 pct of H by number. Galaxies are allowed to form out of the IGM, if the total density and baryonic density satisfy an overdensity criterion. Subsequently, the newly formed galaxies release 10 to the 60th ergs of energy into the IGM over a period of 10 to the 8th years. Calculations have been performed with 32 to the 3rd dark matter particles and 32 to the 3rd cells in a cube with comoving side length L = 9.6/h Mpc. Dark matter particles and galaxies have been followed with an N-body code, while the IGM has been followed with a fluid code
Kinematics and Magnetic Properties of a Light Bridge in a Decaying Sunspot
We present the results obtained by analyzing high spatial and spectral
resolution data of the solar photosphere acquired by the CRisp Imaging
SpectroPolarimeter at the Swedish Solar Telescope on 6 August 2011, relevant to
a large sunspot with a light bridge (LB) observed in NOAA AR 11263. These data
are complemented by simultaneous Hinode Spectropolarimeter (SP) observation in
the Fe I 630.15 nm and 630.25 nm lines. The continuum intensity map shows a
discontinuity of the radial distribution of the penumbral filaments in
correspondence with the LB, which shows a dark lane (about 0.3" wide and about
8.0" long) along its main axis. The available data were inverted with the
Stokes Inversion based on Response functions (SIR) code and physical parameters
maps were obtained. The line-of-sight (LOS) velocity of the plasma along the LB
derived from the Doppler effect shows motions towards and away from the
observer up to 0.6 km/s, which are lower in value than the LOS velocities
observed in the neighbouring penumbral filaments. The noteworthy result is that
we find motions toward the observer up to 0.6 km/s in the dark lane where the
LB is located between two umbral cores, while the LOS velocity motion toward
the observer is strongly reduced where the LB is located between an umbral core
at one side and penumbral filaments on the other side. Statistically, the LOS
velocities correspond to upflows/downflows andcomparing these results with
Hinode/SP data, we conclude that the surrounding magnetic field configuration
(whether more or less inclined) could have a role in maintaining the conditions
for the process of plasma piling up along the dark lane. The results obtained
from our study support and confirm outcomes of recent magnetohydro-dynamic
simulations showing upflows along the main axis of a LBs
Fast Large Volume Simulations of the 21 cm Signal from the Reionization and pre-Reionization Epochs
While limited to low spatial resolution, the next generation low-frequency
radio interferometers that target 21 cm observations during the era of
reionization and prior will have instantaneous fields-of-view that are many
tens of square degrees on the sky. Predictions related to various statistical
measurements of the 21 cm brightness temperature must then be pursued with
numerical simulations of reionization with correspondingly large volume box
sizes, of order 1000 Mpc on one side. We pursue a semi-numerical scheme to
simulate the 21 cm signal during and prior to Reionization by extending a
hybrid approach where simulations are performed by first laying down the linear
dark matter density field, accounting for the non-linear evolution of the
density field based on second-order linear perturbation theory as specified by
the Zel'dovich approximation, and then specifying the location and mass of
collapsed dark matter halos using the excursion-set formalism. The location of
ionizing sources and the time evolving distribution of ionization field is also
specified using an excursion-set algorithm. We account for the brightness
temperature evolution through the coupling between spin and gas temperature due
to collisions, radiative coupling in the presence of Lyman-alpha photons and
heating of the intergalactic medium, such as due to a background of X-ray
photons. The hybrid simulation method we present is capable of producing the
required large volume simulations with adequate resolution in a reasonable time
so a large number of realizations can be obtained with variations in
assumptions related to astrophysics and background cosmology that govern the 21
cm signal.Comment: 14 pages and 15 figures. New version to match accepted version for
MNRAS. Code available in: http://www.SimFast21.or
DIVE in the cosmic web: voids with Delaunay Triangulation from discrete matter tracer distributions
We present a novel parameter-free cosmological void finder (\textsc{dive},
Delaunay TrIangulation Void findEr) based on Delaunay Triangulation (DT), which
efficiently computes the empty spheres constrained by a discrete set of
tracers. We define the spheres as DT voids, and describe their properties,
including an universal density profile together with an intrinsic scatter. We
apply this technique on 100 halo catalogues with volumes of 2.5\,Gpc
side each, with a bias and number density similar to the BOSS CMASS Luminous
Red Galaxies, performed with the \textsc{patchy} code. Our results show that
there are two main species of DT voids, which can be characterised by the
radius: they have different responses to halo redshift space distortions, to
number density of tracers, and reside in different dark matter environments.
Based on dynamical arguments using the tidal field tensor, we demonstrate that
large DT voids are hosted in expanding regions, whereas the haloes used to
construct them reside in collapsing ones. Our approach is therefore able to
efficiently determine the troughs of the density field from galaxy surveys, and
can be used to study their clustering. We further study the power spectra of DT
voids, and find that the bias of the two populations are different,
demonstrating that the small DT voids are essentially tracers of groups of
haloes.Comment: 12 pages, 13 figure
Twist, Writhe & Helicity in the inner penumbra of a sunspot
The aim of this work is the determination of the twist, writhe, and self
magnetic helicity of penumbral filaments located in an inner Sunspot penumbra.
To this extent, we inverted data taken with the spectropolarimeter (SP) aboard
Hinode with the SIR (Stokes Inversion based on Response function) code. For the
construction of a 3D geometrical model we applied a genetic algorithm
minimizing the divergence of the magnetic field vector and the net
magnetohydrodynamic force, consequently a force-free solution would be reached
if possible. We estimated two proxies to the magnetic helicity frequently used
in literature: the force-free parameter and the current helicity term. We show
that both proxies are only qualitative indicators of the local twist as the
magnetic field in the area under study significantly departures from a
force-free configuration. The local twist shows significant values only at the
borders of bright penumbral filaments with opposite signs on each side. These
locations are precisely correlated to large electric currents. The average
twist (and writhe) of penumbral structures is very small. The spines (dark
filaments in the background) show a nearly zero writhe. The writhe per unit
length of the intraspines diminishes with increasing length of the tube axes.
Thus, the axes of tubes related to intraspines are less wrung when the tubes
are more horizontal. As the writhe of the spines is very small, we can conclude
that the writhe reaches only significant values when the tube includes the
border of a intraspine.Comment: 7 pages, 4 figures; Astrophysical Journal, in pres
Solitons in the dark: non-linear structure formation with fuzzy dark matter
We present the results of a full cosmological simulation with the new code
SCALAR, where dark matter is in form of fuzzy dark matter, described by a light
scalar field with a mass of eV and evolving
according to the Schr\"{o}dinger-Poisson system of equations. In comoving
units, the simulation volume is on a side, with a
resolution of at the finest refinement level. We analyse
the formation and the evolution of central solitonic cores, which are found to
leave their imprints on dark matter density profiles, resulting in shallower
central densities, and on rotation curves, producing an additional circular
velocity peak at small radii from the center. We find that the suppression of
structures due to the quantum nature of the scalar field results in an
shallower halo mass function in the low-mass end compared to the case of a
CDM simulation, in which dark matter is expected to cluster at all
mass scales even if evolved with the same initial conditions used for fuzzy
dark matter. Furthermore, we verify the scaling relations characterising the
solution to the Schr\"{o}dinger-Poisson system, for both isolated and merging
halos, and we find that they are preserved by merging processes. We
characterise each fuzzy dark matter halo in terms of the dimensionless quantity
and we show that the
core mass is tightly linked to the halo mass by the core-halo mass relation
. We also show that the core
surface density of the simulated fuzzy dark matter halos does not follow the
scaling with the core radius as observed for dwarf galaxies, representing a big
challenge for the fuzzy dark matter model as the sole explanation of core
formation.Comment: 15 pages, 12 figure
NATIONAL MENTALITY UNDER THE CONDITIONS OF DIGITALIIZATION
The article is devoted to the philosophical analysis of the role of national mantality and cultural codes in the development of digital society. The article explores various approaches to the definitions of the concepts of mentality and national cultural code. The main features of mentality have been analyzed. Among them are the following: 1) the mentality is historically and culturally determined; 2) mentality is a structural part of individual consciousness; 3) mentality is changeable and transforms along with changes of the cultural field. The emphasis is placed on the synergetic approach which most fully takes into account the variability of various elements of culture and the relationship between them. The national code of culture is defined as a system of representations, images and stereotypes of consciousness and behavior, which has a non-hierarchical historical character, reflects national values, and also serves as the basis of national identity. It is emphasized that the national cultural code is closely related to the national value system, reflects it, but is not identical to it, since, unlike the value system, the elements of the cultural code are not hierarchical. Despite its ideal nature, the cultural code influences the material aspects of culture through the motivation of the behavior and activities of its carriers. Along with the national cultural code, the concept of the “cultural code of personality” is being formed in modern scientific literature. The cultural code is not something immutable. It can change under the influence of various factors. The article highlights such trends in the transformation of national cultural codes under the influence of digitalization as universalization, localization and individualization. Today the national cultural code serves as a launching pad for the formation of innovation and individual creativity that transcends national cultural boundaries. It has been concluded that the national cultural code provides a kind of “worldview immunity” against the “dark” side of digitalization without hindering the use of its positive possibilities.Key words: Mentality, Cultural Field, Cultural Code, Values, Consciousness, Economy, Digitalization, Society
Selected Topics in Regulation and Competition
Opportunit\ue0 di pre-funding delle infrastrutture aeroportuali italiane alla luce di un\u2019analisi di benchmarking delle tariffe dei servizi aeroportuali internazionali. The role of the discount rate in cost-benefit analysis between theory and practice: a comparative survey. The harmonization of market entry regulation for the operation of air services in the European Union: a comparative survey of the implementation of Regulation (EC) no. 1008/2008 by member states' authorities. The "dark side" of code-sharing - The anticompetitive effects of code-sharing agreements among airlines
- …